METABOLISM 573 



of the energy liberated in the body does not, however, take the form of heat. A 

 variable amount appears as mechanical work, so that to measure in calories all of the 

 energy that an animal expends, one must add to the actual calories given out, the 

 calorie equivalent of the muscular work which has been performed by the animal dur- 

 ing the period of observation. This can be measured by means of an ergometer, 

 a calorie corresponding to 425 kilogram* meters of work. That it has been possible to 

 strike an accurate balance between the intake and the output of energy of the animal 

 body, is one of the achievements of modern experimental biology. It can be done in 

 the case of the human animal; thus, a man doing work on a bicycle ergometer in the 

 Benedict calorimeter gave out as actual heat 4,833 C., and did work equalling 602 C., 

 giving a total of 5,435 C. By drawing up a balance sheet of his intake and output 

 of food material during this period, it was found that the man had consumed an amount 

 capable of yielding 5,459 C., which may be considered as exactly balancing the actual 

 output. 



It would be out of place to give a full description of the respiration calorimeter here. 

 The general construction will be seen from the accompanying figure of the form of 

 apparatus in use for patients in the Eussell Sage Institute, New York. One of the most 

 icteresting details of its construction concerns the means taken to prevent any loss of 

 heat from the calorimeter to the surrounding air. This is accomplished in the follow- 

 ing way: The innermost layer of the wall is of copper; then, separated from this by 

 an air space, is another wall of copper, outside of which are two wooden walls separated 

 from each other and from the outer copper walls by air spaces. The two copper walls 

 are connected through thermoelectric couples, so that an electric current is set up when- 

 ever there is any difference in their temperatures. The current is observed by means of 

 a galvanometer placed outside the calorimeter, and from its movements the observer 

 either heats up or cools down the outer copper walls so as to correct the difference of 

 temperature causing the current. This is done by an electric heating device or by cold 

 water tubes placed between the outermost copper and the innermost wooden walls. 

 Since the temperature of the two copper walls is the same, there can be no exchange of 

 heat between them, and consequently none of the heat that is absorbed by the inner cop- 

 per walls is allowed to be carried away. All the heat given out by the animal is ab- 

 sorbed by the stream of cold water flowing through the coils of pipe in the chamber. 

 The heat used to vaporize the moisture from skin and lungs must of course also be 

 measured. This is done by collecting the water vapor in a sulphuric-acid bottle placed 

 in the ventilating current. By multiplying the grams of water by the factor for the 

 latent heat of vaporization, we obtain the calories of heat so eliminated. 



' ' The calorimeter contains a comfortable bed and is provided with two windows, a 

 shelf, a telephone, a fan, a light and a Bowles stethoscope for counting the pulse. 

 The ordinary experiment takes about as long as a trip from New York to New London. 

 Patients, as a rule, doze from time to time or else try to work out some scheme by 

 which they can amuse themselves without moving. After three or four hours they are 

 rather bored by the quiet, and the observations are not prolonged beyond this time. 

 They are allowed to turn over in bed once or twice an hour, but reading and telephon- 

 ing are discouraged, since these increase the metabolism. The air in the box is fresh 

 and pure, the patient suffers no discomfort, and objections to the procedure are very 

 infrequent. Most of the patients are only too glad of the extra attention, and they 

 insist that the calorimeter has a marked therapeutic value." (Du Bois.) 



Normal Values. Having thus satisfied ourselves as to the extreme 



*A kilogram meter is the product of the load in kilograms multiplied by the distance in meters 

 through which it is lifted. 



